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Compaction“Victorious warriors win first and then go to war, while defeated warriors go to war first and then seek to win.” —Sun-tzu
Asphalt InstituteMS-22MS 22
Chapter 6-Compaction
What is Compaction?
The process of reducing the volume of a given mass of
material.
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Compaction Illustrated
Compaction
• Vital for Good Performance• Compaction Goal
– 4-8% Air Voids (Conventional Mixes)– 3-6% Air Voids (Coarse or Gap Graded Mixes)
• Requirements for Compaction– Compactive Effort
• Use the right rollers– Good Mix Temperatures (Workable)
• Haul length• Ambient conditions
– Mixture Confinement• Lift thickness• Base support
Compaction Goals
• Increase stability
• Reduce air voids
• Provide a smooth surface
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Factors Affecting Compaction
• Mixture properties
• Ambient conditions
• Lift thickness
• Base/subgrade support (confinement)
• Compactive effort
Factors Affecting Compaction
• Mixture properties
• Ambient conditions
• Lift thickness
• Base/subgrade support (confinement)
• Compactive effort
Mixture Properties
• Materials characteristics– Asphalt binder
– Aggregates
Mi d i• Mix design – Aggregate structure
– Volumetric properties
• Production variables– Moisture content
– Temperature
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Asphalt Binder Properties
• Binder grade– Increase high temperature grade stiffer binder
– Neat or modified?• PG grades with 92°C or more temperature difference are
ll l difi dusually polymer modified
• Temperature– Must complete compaction while mix temperature
exceeds:• 85°C (185°F) for neat binders
• 100°C (212°F) for modified binders
• 70°C (155°F) for warm mix binders?
Polymer-Modified Asphalt
• Stiffen at much higher temperatures than neat asphalt– Reduce time available for compaction by half
When specifying binders that will likely be• When specifying binders that will likely be polymer-modified (PG 70-28, PG 76-22, etc.)– Avoid requiring compacted lift thickness less
than two inches
Aggregate Properties
• Physical properties– Gradation
– Angularity
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AngularAggregate
Contrasting Stone Skeletons
RoundedAggregate
Mixtures designed to resist rutting will also resist compaction!!!Mixtures designed to resist rutting will also resist compaction!!!
Compaction
• Moisture Content– Lubricants tenderness
– Most common with:• Drum plants
• Mixes with RAP
• Absorptive aggregates
• Stockpiles that have been sitting
Compaction
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Factors Affecting Compaction
• Mixture properties
• Ambient conditions
• Lift thickness
• Base/subgrade support (confinement)
• Compactive effort
Ambient Conditions
Mat Thickness Base Temperatures (Minimum)
Degrees F Degrees C
3 inches or greater 40 43 inches or greater 40 4
1-3 inches 45 7
Less than 1 inch 50 10
AK specs—40°F and rising
Factors Affecting Compaction
• Mixture properties
• Ambient conditions
• Lift thickness
• Base/subgrade support (confinement)
• Compactive effort
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Compaction
• Temperature– Generally – hotter is better
– But – heat ages the mixture
– Thicker lift holds heat better• An extra 1.0 cm gains 6-7 minutes of
compaction time
• Generally – lift should be three times the nominal maximum aggregate size
30
20Com
pact
ion,
min -1°C16°C32°C
MS-22, Table 6.03
20
10
025 50 75 100
Tim
e av
ail.
for
C
Compacted Thickness, mm
Mix Temp. = 135°C
30
20Com
pact
ion,
min -1°C16°C32°C
MS-22, Table 6.03
Increasing the lift thickness by 1.0 cm adds 20
10
025 50 75 100
Tim
e av
ail.
for
C
Compacted Thickness, mm
y6-7 minutes to available
compaction time.
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Suggested Lift Thickness Ranges, P-401 (FAA)
Max. Aggregate Size
Suggested Lift Thickness, in
minimum maximum
1¼ inch 3 6
1 inch 2½ 41 inch 2½ 4
¾ inch 1¾ 3
½ inch 1½ 2½
Do not specify lifts thinner than 1½ inch (40 mm)
AK Specs??
Factors Affecting Compaction
• Mixture properties
• Ambient conditions
• Lift thickness
•• Base/subgrade support (confinement)Base/subgrade support (confinement)
• Compactive effort
Confinement
• Stable platform
• Good grip on underlying surface– Clean surface
P l t k d– Properly tacked
• Use temperature to confine edges– Delay rolling unsupported edge to allow
“internal confinement” to develop
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Factors Affecting Compaction
• Mixture properties
• Ambient conditions
• Lift thickness
• Base/subgrade support (confinement)
•• Compactive effortCompactive effort
Compaction Equipment
• Screed– Screed weight– Screed vibration– Tamper barp
• Rollers– Vibratory steel– Pneumatic– Static steel– Combination
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Tamper Bar
Moves up and down tamping mix under the screed
Rolling Procedures
• Breakdown rolling– Provides nearly all
needed density
• Intermediate rollingg– Provides final density
level– Seals surface
• Finish rolling– Removes roller marks
Rollers
• Vibratory– Used for
breakdown (initial) compaction
– Offers greatest compactive effort
– Speed of roller needs to match its frequency
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Amplitude & Frequency
Time between blows, t
amplitudeF = 1/t
Amplitude = f (drum weight, eccentric moment, frequency)Amplitude is calculated, not measured value.
Checking Frequency
Contractors and Inspectors should have a Reed Tachometer available
Vibratory Rollers
• Commonly used for initial (breakdown) rolling• 8-18.5 tons, 57-84 in wide (“heavy” rollers)
– 50-200 lbs/linear inch (PLI)
• Frequency: 2700 - 4200 impacts/min.– Trend to increase frequency
• Amplitude: 0.4 - 0.8 mm– For thin overlays (< 150 mm) use lowest amplitude
setting or static mode
• Operate to attain at least 30 impacts/meter– 3-6.5 km/hr
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Why are vibratory rollers more effective?
• Movement of drum initiates particle motion
• Resistance to deformation is much less when particles are moving than when static (inertia)static (inertia)
• Force applied by weight of drum has greater effect, thus achieving more compaction per pass than other roller types
Roller Speed Comparison
95
100
ity
1 7 MPH
80
85
90
0 1 2 3 4 5
Number of Passes
Den
si 1.7 MPH
2.8 MPH
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Frequency vs. Travel Speed
VPM 2 mph 2.5 mph 3 mph 3.5 mph 4 mph
2000 11.4 --- --- --- ---
2500 14.2 11.4 --- --- ---
3000 17.0 13.3 11.4 --- ---
3500 19.9 15.9 13.3 11.4 10.0
4000 22.7 18.2 15.2 13.3 11.4
What happens if you operate the roller too fast?
• < 10 impacts per foot causes separated impacts
• Result is a washboard/rippling
tt th t ’t bpattern that can’t be rolled out
• Most easily seen with low-angle light – Early or late in day– Headlights from
vehicles
Pneumatic Roller
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Rubber Tire Manipulation
• Overlap manipulates mat under and between tire
• Tight finish resists moisture penetration
• Manipulation increased by lowering tire pressure
• Static force increased by high tire pressure
Pneumatic Roller
• Generally used as intermediate roller
• Reorients particles through kneading action
• Load/tire: 1050 – 6730 #/tire depending on model/ballastmodel/ballast
• Tire pressure of ~70 psi—must be consistent
• Be sure to ballast
• Tires must be hot to avoid pickup
• Use skirts
Compaction Issues - Tire Pick-up
• Once tires hot -keep them hot
• Develop good rolling pattern -never stopnever stop rolling
• If waiting for trucks, roll on previously compacted mat
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Static Steel-Wheeled Rollers
• 10-14 ton rollers normally used for HMA compaction– Commonly use vibratory
rollers operated in static modemode
• Lighter rollers used for finish rolling
• Drums must be smooth and clean
• For initial compaction, drive wheel must face paver
AI MS-22, Figure 6.05
Test (Control) Strip
• At least 300 feet long, two “pulls” wide
• Closely Simulate Paving Conditions– Base conditions
– Haul times– Haul times
– Mixture storage
– Paver speed
– Joint construction
• Monitor Compaction After Each Pass– Density will climb, then peak, then fall
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ity
Establishing Rolling Pattern
Den
si
0 1 2 3 4 5
# Passes
Rolling Pattern
• Speed & lap pattern for each roller
• Number of passes for each roller– One trip across a point on the mat
• Minimum temperature by which each roller mustMinimum temperature by which each roller must complete pattern
IMPORTANT:Paver speed must not exceed that of the
compaction operation!!!
General Rules
• Avoid Stopping and Sitting on Hot Mat
• Never Turn a Stopper Roller
• Angle all Stops
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Improving Quality Control with
Intelligent CompactionBuild a better mousetrap and the world will beat
a path to your door.- Ralph Waldo Emerson
How Does IC Help with QC?
• “Real-Time” Feedback to Roller Operator– On-Board, Color-Coded Mapping
• Improved roller patterns
• Improved temperature control
• Ability to make adjustments “on-the-fly”
• Permanent Records of Compaction Data
• “Mapping” of Underlying Materials– RMV (Roller Measurement Values) readings
• Locates “soft spots”
• Identifies irregular support for compaction
• Proper in-place density is vital for good performance
Why Do We Need IC?
Why Intelligent Compaction?
• Conventional compaction equipment and procedures have shortcomings and too often produce poor results
• Intelligent compaction technology appears to offer “a better way”
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Improving QC with IC
• Shortcomings in Density Acceptance Process…
Limited Number of Locations After Compaction is Complete
MN
IN
NY
PA
MD
ND
WI
IC Pooled Fund (ICPF)
KS
TXMS
INVA
GA
2008
2009
2010
ICPF States / Year
What is Intelligent Compaction?
Vibratory Single Drum Soil Roller
Vibratory Tandem Drum Asphalt Roller
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IC Roller Requirements
• IC Roller Requirements– Roller Measurement Value (RMV)
– GPS-Based documentation system
– Color-coded display (on-board)
– Surface temperature measurement system
– Optional: automatic feedback system
Color-Coded On Board Display
Global Positioning System (GPS)
GPS Base StationGPS Base Station GPS Radio & ReceiverGPS Radio & Receiver GPS RoverGPS Rover
Real Time Kinematic (RTK) GPS Precision
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Mat Surface Temperature Measurement
Infrared Thermal Gauge
“Real-Time” Feedback to Roller
Improving QC using IC
Real-Time Feedback to Roller Operator
• Roller Passes
Shoulder (Supported)Paving Direction
Sakai Project - CA
Longitudinal Joint
Shoulder (Supported)
Courtesy Sakai AmericaCourtesy Sakai America
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Roller Operator Training
Improved Rolling Patterns Before
AfterAfter
Sakai IC roller
Indiana ICPF Project
Permanent Records of
Improving QC using IC
Compaction Related Dataand Data Analysis
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“Mapping of Underlying Layers
Improving QC using IC
Mapping of Underlying Layers Prior to Paving
“Mapping” of Underlying Materials
• Use of RMV color-coded mapping to measure support prior to paving of:– Subgrade soil materials
Stabilized subbase materials– Stabilized subbase materials
– Aggregate base materials
– Existing asphalt pavements
– Rubblized concrete pavements
• Underlying Support affects compatibility of subsequent layers
Mapping of the subgrade / agg. base layer
“Mapping” of underling layers
Minnesota ICPF Project
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Future Research Needs - IC
• Improve correlation of Density vs. RMV
• Standardization of RMV
• Explore GPS TechnologyUse of advanced high prec GPS technology– Use of advanced, high prec. GPS technology
– “Stand-Alone” (non RTK) GPS Technology
• IC Data Management– Improvements in on-board roller software
– Data collection/storage
– Data analysis/reporting
Summary
• Intelligent Compaction is a major innovation in compaction technology
• Research/field projects show that IC can offer a valuable tool to improve QC of theoffer a valuable tool to improve QC of the compaction process
• IC technology is now readily available in U.S.
• More work is need to address various issues
• Stay tuned!
We’ve Come a Long Way
1924 Buffalo Springfield Steam Roller
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Questions?
